A reliable marking or inscribing of glass or glass products is becoming increasingly important, e.g. for marking glass batches or products made of glass, for example for tracking purposes. In particular also tamper-proof marks in or on glass may be desirable to ensure an original quality, for example, in primary packaging made of glass, for example in the form of glass vials for the pharmaceutical industry.
Recently laser radiation is increasingly used for marking or inscribing of glass. Such methods are very clearly described in the introductory part of the description of the German patent application DE 102 34 002 A1 of the applicant, the content of which is hereby expressly incorporated herein by reference for purposes of disclosure. Such methods, however, often require particular measures, which are typically expensive.
The German patent DE 101 22 335 C1 (corresponding to U.S. patent application US 2003/0029849 A1) of the applicant discloses a method and apparatus for marking glass with a laser in which by thermal impact on the surface of the glass to be marked a mark is provided on the surface of the glass. The marks are in this case formed at high temperatures above the transformation temperature of the glass, for example in a tube-drawing plant during the production of glass tubes.
German patent application DE 102 34 002 A1 of the applicant discloses a similar method in which the mark is formed by one or more local deformations of the surface of the glass, which respectively implement a lens effect.
WO 2009/128893 A1 discloses a laser ablation method for forming microstructure cavities in the surface of a glass substrate for applications, such as micro-fluidic systems, providing hyper-hydrophobic surfaces, micro cavity arrays, micro-lens systems, cells for life science applications and providing of micro-mixing reactors. Disclosed is a first embodiment in which a first plurality of laser spots are set along a first line, and then a further plurality of laser spots are set along a second line which is parallel to the first line. Disclosed is also a second embodiment, in which a continuous series of laser spots overlapping with each other are formed line-wise in dense intervals and in a “stuttering” manner, namely in crosswise geometry. The laser spots overlap each other. The microstructure-cavities in the surface of a glass substrate are formed by laser ablation. It is not important, however, whether mutually adjacent laser spots are set simultaneously or sequentially to each other. Rather, the opening diameter and the shape of the micro-structure cavities to be formed in the surface of the glass substrate are adjusted by means of the distance between the laser spots to each other and by means of the overlap of the laser spot to each other.
In particular for forming complex marks consisting of many marking points a high amount of energy needs to be deposited in the glass within a relatively short period, which may still lead to a weakening of the material, for example to micro-cracks, despite the formation of the marks at temperatures above the transformation temperature of the glass.